Various heterogeneous immunoassays for the detection and quantification of analyte molecules in a liquid sample are known, and several employ the displacement of a labeled moiety from an insoluble support.
In this regard, U.S. Pat. No. 4,330,299 is of interest for disclosing a method for measuring the level of glucose in animal body fluids which comprises contacting a portion of a given body fluid with a glucose indicator comprising a reversible complex of a carbohydrate component, a binding macromolecular component, and an indicator element bound to one of the components. The sample of body fluid is maintained in contact with the glucose indicator for a period of time sufficient to permit the glucose present to displace the carbohydrate component in the reversible complex, whereby the indicator element is released to signify the presence of glucose. This assay suffers from the disadvantage that its applicability is restricted to glucose and other sugars.
U.S. Pat. No. 4,425,438 discloses an assay method and flowthrough test device in which test substance may displace an analytical reagent, which can be the test substance chemical labeled with a detectable group and with a group capable of binding specifically to an analytical absorbant, from a primary absorbant. A column is provided with two zones, a primary absorbant zone and an analytical absorbant zone, through which the assay fluid, admixed with a predetermined quantity of analytical reagent, is sequentially passed. Any analytical reagent not bound by the primary absorbant substance becomes bound to the analytical absorbant substance. The presence of analytical reagent bound to the analytical absorbant substance is then determined. A principal disadvantage of this assay is that the specific amounts of primary absorbant in the primary absorbant zone and of analytical reagent mixed with the assay fluid must be carefully balanced to ensure that no analytical reagent will pass through the beads if no test substance is present, and, at the same time, at least some analytical reagent will pass through the beads if test substance is present in the assay fluid.
U.S. Pat. No. 4,434,236 discloses an immunoassay wherein labeled antibody having greater affinity for analyte in the fluid sample than for immobilized analyte-analog is displaced from the solid phase. A principal disadvantage of this assay is that the fluid sample containing displaced labeled antibody must be analyzed by means, such as by spectrophotometer or fluorometer, that do not lend themselves to home or field use. Another disadvantage is that labeled divalent antibodies cannot be accurately employed in this assay.
Immunoassays based upon competitive binding between a targeted analyte and a labeled analyte reagent, for available analyte-specific binding sites on an insoluble support, have also been described.
While perhaps advantageous for certain applications, few or none of the prior art devices and methods provide a single-step, self-contained test device that can be conveniently used by a nontechnical user for on-site testing. It would also be advantageous to provide an integrated device that can be conveniently manufactured and used to detect and quantify the presence of several different analytes in a single application, preferably for real-time testing.